Piston for injection type internal combustion engines

ABSTRACT

A piston for injection type internal combustion engines, which has the bottom surface forming part of the main combustion chamber provided with a piston chamber in which an insert member defining a supplemental combustion chamber is inserted while an intermediate member is interposed between said insert member and the piston body portion defining said piston chamber, said intermediate member having zones of constant or different thermal conductivities according to a predetermined heat pattern.

I United States Patent 11 1 1 1 357309163 Elsbett et a1. May 1, 1973PISTON FOR INJECTION TYPE 2,873,727 2 1959 Meurer 123 32 B INTERNALCOMBUSTION ENGINES 2.942.591 6/1960 Meurer... 3,221,722 121965 B h] [751Invenmm Elsbe"; Pudwig Elsbefi, 3,251,349 5/1966 151: both of1111138115161", Germany 3,402,644 9/1968 Geiger e161. ..92/224 [73]Assignee: Maschinenfabrik Augsburg-Nurn- F I N A E T P L N bergAktiengesellschaft Werk Num- ORE G P T N SOR A p ICATIO S berg,Nurnberg, Germany 551,993 11/1956 Belgium ..123/32 B 1,288,819 2/1962France Flledi 1"- 7, 1971 1,122,325 1/1962 Germanyw 1,157,428 11/1963'Germany.... [211 App] 132094 553,161 12/1956 Italy ..123/32 B [30]Foreign Application Priority Data Primary Examiner-Wende11 E. Burns Apr.7, 1970 Germany ..P 20 16 386.4 Ammey walter Becker 52 us. 01. ..123/193 P, 92/213, 92/224, [571 ABSTRACT 123/32 B, 123/41-35 A piston forinjection type internal combustion en- 1 1102f F021 F gines, which hasthe bottom surface forming part of of Search P, B, the combustionchamber provided a piston 123/32 191 92/213, 1 108, chamber in which aninsert member defining a supple 224 mental combustion chamber isinserted while an intermediate member is interposed between said insert[56] References cued member and the piston body portion defining saidUNITED STATES PATENTS piston chamber, said intermediate member hayingzones of constant or dlfferent thermal conductlvltles 2,832,325 4/1958Liebe1 ..L ..123/32 B according to a predetermined heat pattern.2,865,346 12/1958 Liebel.... 123/32 B 2,870,754 1/1959 Morris 123/32 B11 Claims, 2 Drawing Figures lb 1 4 5a Patented May 1, 1973,

-i FIG- l INVENTORS GUNTER ELSBETT LUDWIG ELSBETT PISTON FOR INJECTIONTYP-E INTERNAL COMBUSTION ENGINES This invention relates to an improvedpiston for injection-type internal combustion engines, in particularDiesel engines, having an insert in the combustion chamber designed toretain unburned fuel particles.

It has long been the aim of engine designers and, in particular, Dieselengine designers, to ensure a complete combustion of the fuel introducedinto the combustion chambers in order in this manner to prevent toxicand/or obnoxious exhaust emissions. Complete combustion is understood tobe a process which after the energy process conversion will leave onlyinert substances that will not undergo any further reactions. In orderthat this may be achieved, it is important that the fuel and all fuelconstituents contained in it are burned in the combustion spaces at suchan optimum temperature as will positively ensure oxidation andinertization of all fuel constituents. However, maintaining an optimumtemperature frequently fails because, on the one hand, the engines arerarely operated at a constant speed and, consequently, constant load,while, on the other hand, control of the temperatures in the combustionchamber by its walls is not load-dependent or temperature-dependentrespectively.

With a view to achieving control of the temperature in a combustionchamber according to a predetermined heat distribution pattern in spiteof the fluctuating load of the engine, combustion chambers of thespherical type have been provided with a cavity into which a fluid isinjected at a rate which is varied according to the desired degree oftemperature control of the combustion chamber. This fluid enters thecavity at one point and leaves the cavity at another point. This knownarrangement has the drawback that nonuniform temperature control of thecombustion chamber wall occurs because the fluid introduced undergoes atemperature change between the entrance into the cavity and its exitand, apart from that, fuel constituents tend to condense on the colderportions of the combustion chamber wall. Condensationof these fuelconstituents prevents complete combustion and, as a result, obnoxiousemissions are liable to result.

According to another known method of controlling 'the' temperature ofthe combustion chamber in the piston, the combustion chamber issurrounded by a number of chambers containing substances designed toprovide temperature control of the combustion chamber walls. Thesechambers, which may for instance be cylindrical and may be arrangedaround the longitudinal axis of the piston are filled only partly withthe respective substance, leaving space for its expansion. The substancemay consist, inter alia, of metals that are liquid when hot and form anefficient heat transmission agent'in this state, whereas in the coldstate they may also be liquid, such as mercury, or solid such as sodium.It is considered to be a drawback of this method of temperature controlthat producing the chambers around the combustion chamber involves avery high amount of labor, due to the fact that the individual chambershave to be made individually and have to be filled and sealedindividually. In addition thereto, between the chambers there remainribs around the combustion chamber which will not, or only partly, beinfluenced by the temperature control of the substance. A furtherdrawback may be seen in the fact that when the engine is in a tiltedposition, the temperature distribution pattern will change inasmuch asthe liquid substance will wander according to the tilted position of theengine to provide temperature control, i.e., cooling, for portions ofthe combustion chamber wall that may not require cooling so urgently asother portions of the wall at the opposite side and vice versa.

Another known method of controlling heat dissipation from the combustionchamber of an internal combustion engine consists in having a sphericalcombustion chamber partly surrounded. by a ring-shaped insert embeddedin the piston head. Covering part of the combustion chamber wall, thisring insert, which alternately serves to dissipate heat from thecombustion chamber or prevent dissipation from it, consists of asubstance the thermal conductivity of which increases as its temperatureincreases and, conversely, decreases as its temperature decreases, suchas for instance, chrome nickel steel with 18 percent chromium contentand 8 percent nickel content. While this ring insert does in factprovide a certain measure of temperature control of the combustionchamber and, consequently, of its walls, it is not possible with thismethod to prevent unburned fuel constituents from leaving the combustionchamber as these are drawn out of the combustion chamber during thepower stroke of the engine.

In order to be able to regulate temperature control of the combustionchamber in the piston of a compression ignition engine according to anoptimum heat distribution pattern, it has also been proposed to installan insert in the combustion chamber in the piston and to provide thisinsert with a baffle at its end facing the cylinder extending towardsthe axis of rotation of the combustion chamber (this being formed in theshape of a solid of revolution). The baffle is provided with a rimextending towards the axis of the combustion chamber in a manner that astraight line tangent to its rim will intersect the axis preferably nearthe bottom of the combustion chamber. The provision of the insert with abatfle causes fuel constituents, which enter the combustion chamber witha swirling motion and are deposited due to the centrifugal action on thewallsof the insert, to be retained in the combustion chamber until theyhave been heated to such an extent as to cause optimum oxidation andelimination of obnoxious emissions from the combustion chamber in thepiston. In order to bring about such optimum oxidation of the fuelconstituents retained, these constituents are allowed to leave thecombustion chamber only after passing the rim of the baffle with theresult that, as the combustion gases flow past the baffle rim, thesefuel constituents are exposed to considerable heating by the very hotbaffle rim. Owing to the primary heating of the fuel constituents on theinsert surfaces and subsequent heating at the rim of the baffle, anyentrained unburnt constituents will be heated to the necessary hightemperature and completely burnt. With a view to ensuring efficientcombustion which is the sole factor controlling obnoxious emissions andwhat is commonly called blue smoke, it is an advantage if, in additionto the baffle, means are provided for temperature control of the insert.

It is an object of the present invention to provide control of thetemperature of the insert placed in the combustion chamber so that itswalls will have the necessary temperatures in the various zones of thecombustion chamber for efficient combustion to result.

In a piston of the above described type, this object has been realizedby providing an intermediate member having locally constant or varyingthermal conductivities between the insert and the ring groove portion ofthe piston so as to provide temperature control of the combustionchamber according to a preset heat distribution pattern.

For ease of production, it will be an advantage according to a furtherfeature of the invention to compose the intermediate member of at leasttwo ringshaped members, the one controlling the combustion chamberbottom having a high or intermediate thermal conductivity and the othercontrolling the baffle having a low thermal conductivity.

According to yet another feature of the invention, the intermediatemember may be split along the contour of the insert with the part of theintermediate member facing the combustion chamber having a high thermalconductivity whereas the parts of the intermediate memberadjacent to thepiston crown have a low thermal conductivity.

The invention is illustrated by way of example in the accompanyingschematic drawing, in which:

FIG. 1 shows the piston head with a spherical combustion chamber and aninsert provided in this combustion chamber; and

FIG. 2 shows a piston head with a spherical combustion chamber and aninsert provided in it formed with a baffle around its throat and anintermediate member placed between said insert and the ring-grooveportion of the piston.

The conical chamber 1 of a piston 2 for internal combustion engines, inparticular compression ignition engines, is provided with an insert 3lining the inner wall surface of an intermediate member 5 inserted insaid chamber 1 and interposed between the latter and said insert 3. Theinner surface of insert 3 defines the spherical combustion chamber la ofthe piston 2. Both the insert 3 and the intermediate member 5 take theshape of annular solids of revolution and are attached to the pistonhead in a manner that they form the wall of the spherical combustionchamber la in the piston 2.

In accordance with the embodiment illustrated in FIG. 1, the insert 3 isformed with a large throat area through which the combustion chamber lacommunicates with the cylinder space. The intermediate member 5,provided betweenthe insert 3 and the body of the piston 2, decreases inthickness from the top downwards and is supported with its thin end atthe bottom-7 of the combustion chamber la. The throat end of theintermediate member 5 is covered by a ring flange 8 of the insert 3which is connected to the body 4 of the piston 2 in any suitablestandard manner. De pending on the desired heat distribution pattern inthe combustion chamber la and, consequently, in the combustion chamberwalls, the intermediate member 5 may be of a material having a high, lowor intermediate thermal conductivity. In order to meet this requirement,the intermediate member 5 is preferably made of carbon substance whichby transformation into graphite can be readily provided with differentdegrees of thermal conductivity. The transformation of the carbon intographite may be effected by heating the carbon, when graduated heatingwill provide the desired graphite structure. For ease of production, itmay be an advantage to design the intermediate member as com posed oftwo ring-shaped sections, each section being provided with the necessarythermal conductivity. For instance, the lower part may have a highthermal conductivity, whereas the upper, i.e., the part adjacent to thepiston crown, may have lower thermal conductivity. The interface betweenthe substances of high and low thermal conductivities naturally need notlie in a horizontal plane, in fact, any desired zoning can be adopted inthe intermediate member 5.

The embodiment illustrated in FIG. 2 differs from the one shown in FIG.1 primarily in that the insert 3b is provided with a baffle 9 around itsthroat, the rim 10 of said baffle being directed towards the interior ofthe combustion chamber 1b in such a manner that a corner 11 is formedbelow the rim of the baffle between the baffle and the insert wall 12.The baffle rim 10 directed into the combustion chamber 1b may be flareddownwards far enough for a straight line y which is tangent to thebaffle rim to intersect the axis x of the combustion chamber 1b near thebottom 7b of the latter. In order to be able to retain any incompletelyburnt fuel constituents in the combustion chamber 1b, it is necessarythat the straight line y which is tangent to the rim l0 intersects theaxis x inside the combustion chamber. With the baffle 9 designed withthis form, any unburnt fuel constituents which due to the action ofcentrifugal forces tend to deposit on the walls of the insert 3 will bepositively forced to rise gradually due to their inertia in thecombustion chamber lb and to leave the same past the rim 10 of theinsert baffle. Since the intermediate member 5 of the combustion chamber1b and, consequently, the insert 3b and the walls 12 can be controlledto suit the desired heat distribution pattern, it is possible, by theuse of low thermal conductivity material for the intermediate member 5,to reduce temperature dissipation through the wall areas adjacent to thethroat of the combustion chamber 1b so that these areas will attain thedesired high temperature for optimum combustion of the unburntconstituents of the fuel. The physical construction of the intermediatement described and provided with thermal conductivities as indicatedthere.

As will be evident from the above, the features characterizing thepresent invention enable temperature control of the walls of the insertto be obtained according to the high or low thermal conductivity of theintermediate member in conformity with the desired heat distributionpattern. This makes it possible for the fuel constituents depositing onthe walls of the combustion chamber to be heated to the optimum level ata faster rate, which is essential in high-speed internal combustionengines. As will also be evident from the foregoing description, inorder to achieve the desired pattern of temperature control, theintermediate member may be provided with different heat conductivitiesin different areas. According to the present invention such zonedthermal conductivities can be achieved in a straightforward manner bymaking the intermediate member of a carbon substance. Carbon offers anadvantage for this purpose in that it can be imparted different thermalconductivities in a simple manner because heating will transform carboninto, say, graphite, which has a high thermal conductivity, whereas ifleft as carbon it will have a poor or lower thermal conductivity.

An advantageous development of the invention consists in making theintermediate member near the level of the combustion chamber throat orclose to the baffle with a low thermal conductivity, while in the areaof the combustion chamber bottom or the far end of the insert it is madewith a high or intermediate thermal conductivity.

It is, of course to be understood that the present invention is, by nomeans, limited to the specific shapes shown, but also comprises anymodifications within the scope of the appended claims.

What we claim is:

1. A piston for injection type internal combustion engines, especiallycompression ignition engines, which has that side of its piston bottomwhich is intended in part to define the main combustion chamber providedwith an axial chamber, and which includes an intermediate memberinserted in said axial chamber andhaving zones of thermal conductivitieswith a predetermined heat distribution pattern, and an annular insertmember for holding back unburned fuel material and so tempered toprovide temperatures necessary for optimum combustion as inserted intosaid intermediate member and lining the inner surface thereof, that sideof said annular insert member which faces the axis of said pistondefining a substantially spherical supplemental combustion chamber openat both ends in axial direction of said piston and substantially coaxialwith said piston.

2. A piston according to claim 1, in which said intermediate member hasdifferent thennal conductivities.

3. A piston according to claim 1, in which said intermediate member hasconstant thermal conductivities.

4. A piston according to claim 1, in which said intermediate member ismade of carbon.

5. A piston according to claim 1, in which said supplemental combustionchamber has that end thereof which is adjacent said piston bottom sidein part defining the main combustion chamber provided with a throat, andin which said intermediate member hasa low thermal conductivity aroundsaid supplemental combustion chamber throat and has a higher thermalconductivity in the region of that end of said supplemental combustionchamber which is remote from the piston bottom surface intended in partto define the main combustion chamber.

6. A piston according to claim 1, in which said supplemental combustionchamber has that end thereof which is adjacent said piston bottom sidein part defining the main combustion chamber provided with an inwardlycurved flange forming an annular baffle, and in which said intermediatemember has a relatively low thermal conductivity in the vicinity of saidbaffle and has a higher thermal conductivity at that end portion of saidsupplemental combustion chamber which is remote from said baffle.

7. A piston according to claim 1, in which said intermediate member iscomposed of a plurality of superimposed annular bodies respectivelyhaving different thermal conductivities, the lower therrnal conductivityof said intermediate member being m the vlcmlty of that piston bottomside which is intended in part to define the main combustion chamber.

8. A piston according to claim 1, in which said intermediate member hasan interface dividing said intermediate member along the contour of theinsert, that part of the intermediate member which is adjacent saidsupplemental combustion chamber having a relatively high thermalconductivity, and another part of said intermediate member which isadjacent the piston body proper having a relatively low thermalconductivity.

9. A piston according to claim 4., in which the thermal conductivity ofthe carbon of said intermediate member is graduated so that a relativelyhigh thermal conductivity prevails adjacent said insert member, and alower thermal conductivity exists perpendicular to the piston axis.

10. A piston according to claim 9, in which to remove combustion chamberheat said relatively high thermal conductivity exists in the axialdirection of said piston.

11. A piston according to claim 1, in which said intermediate memberwhile having zones of different

1. A piston for injection type internal combustion engines, especiallycompression ignition engines, which has that side of its piston bottomwhich is intended in part to define the main combustion chamber providedwith an axial chamber, and which includes an intermediate memberinserted in said axial chamber and having zones of thermalconductivities with a predetermined heat distribution pattern, and anannular insert member for holding back unburned fuel material and sotempered to provide temperatures necessary for optimum combustion asinserted into said intermediate member and lining the inner surfacethereof, that side of said annular insert member which faces the axis ofsaid piston defining a substantially spherical supplemental combustionchamber open at both ends in axial direction of said piston andsubstantially coaxial with said piston.
 2. A piston according to claim1, in which said intermediate member has different thermalconductivities.
 3. A piston according to claim 1, in which saidintermediate member has constant thermal conductivities.
 4. A pistonaccording to claim 1, in which said intermediate member is made ofcarbon.
 5. A piston according to claim 1, in which said supplementalcombustion chamber has that end thereof which is adjacent said pistonbottom side in part defining the main combustion chamber provided with athroat, and in which said intermediate member has a low thermalconductivity around said supplemental combustion chamber throat and hasa higher thermal conductivity in the region of that end of saidsupplemental combustion chamber which is remote from the piston bottomsurface intended in part to define the main combustion chamber.
 6. Apiston according to claim 1, in which said supplemental combustionchamber has that end thereof which is adjacent said piston bottom sidein part defining the main combustion chamber provided with an inwardlycurved flange forming an annular baffle, and in which said intermediatemember has a relatively low thermal conductivity in the vicinity of saidbaffle and has a higher thermal conductivity at that end portion of saidsupplemental combustion chamber which is remote from said baffle.
 7. Apiston according to claim 1, in which said intermediate member iscomposed of a plurality of superimposed annular bodies respectivelyhaving different thermal conductivities, the lower thermal conductivityof said intermediate member being in the vicinity of that piston bottomside which is intended in part to define the main combustion chamber. 8.A piston according to claim 1, in which said intermediate member has aninterface dividing said intermediate member along the contour of theinsert, that part of the intermediate member which is adjacent saidsupplemental combustion chamber having a relatively high thermalconductivity, and another part of said intermediate member which isadjacent the piston body proper having a relatively low thermalconductivity.
 9. A piston according to claim 4, in which the thermalconductivity of the carbon of said intermediate member is graduated sothat a relatively high thermal conductivity prevails adjacent saidinsert member, and a lower thermal conductivity exists perpendicular tothe piston axis.
 10. A piston according to claim 9, in which to removecombustion chamber heat said relatively high thermal conductivity existsin the axial direction of said piston.
 11. A piston according to claim1, in which said intermediate member while having zones of differentthermal conductivities form one single integral piece.